Strain locked nozzle for recoilless weapons



'NOV- 1965 F. w. DIETSCH ETAL 3,215,041

STRAIN LOCKED NOZZLE FOR RECOILLESS WEAPQNS Filed April 30, 1964 2 SheetsSheet 1 1965 F. w. DIETSCH ETAL 3,

STRAIN LOCKED NOZZLE FOR RECOILLESS WEAPONS Filed April 30, 1964 2 Sheets-Sheet 2 Fig, 5

0 2 MS 4M5 7M8 IONS INVENTORS. FRANCIS W. DIETSCH ANDREWJ. GRA DY ATTO RNEYS United States Patent "ice 3,215,041 STRAIN LOCKED NOZZLE FOR RECOTLLESS WEAPONS Francis W. Dietsch, Levittown, and Andrew J. Grandy, North Hills, Pa, assignors to the United States of America as represented by the Secretary of the Army Filed Apr. 30, 1964, Ser. No. 364,041 Claims. ((31. 89-1.7) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to recoilless guns and has for an object to increase the rate of fire and to minimize the Weight and mechanical complexities of such weapons. Another object is to increase the useful life of these guns.

Since recoilless weapons have demonstrated their practicability, they have become of increasing importance during the last fifteen years or more. One object has been their short life due to rapid wear at the constricted throat portion of the venturi nozzle carried by such guns. According to this invention that constricted throat is made for attachment to a round of fixed ammunition in a man ner easily attached to each round by screw threads and in other ways for quick attachment and separation from the round when fired. Such nozzles may be made of light weight steel or other materials for attachment in the field, and reused on subsequent rounds or not as desired. The gun, having no heavy breech with a nozzle, is lighter.

Referring to the drawings:

FIG. 1 illustrates a separable nozzle fixed to the rear end of a round and located in the rear end of a gun before being fired.

FIG. 2 shows the same nozzle when the projectile is ready to be started forward under propellant pressure but with the nozzle expanded into its locking groove.

FIG. 3 corresponds to FIG. 2 except that the projectile has become disengaged from the nozzle which is fully locked under a near peak pressure in the gun.

FIG. 4 has the nozzle relaxed and ready to be ejected rearwardly under residual pressure in the gun.

FIG. 5 exemplifies a typical pressure-time graph such as occurs in the forward end portion of a nozzle secured to a gun.

FIG. 6 is a view corresponding to FIG. 3 except that a cam surface is on the projectile rear instead of an ordinary screw thread.

In FIG. 1 is shown the rear end portion 10 of a breechless, recoilless gun having a projectile 11 therein with the usual boom 12 around which is placed a usual propellant 12a, which may be surrounded by a consumable or combustible case 12b. The projectile is of a type having stabilizing fins 13 which rotate at a low rate for stabilizing the projectile by both fins and a low spin rate. A venturi nozzle 14 is secured to the rear end of the fin periphery by a mating pair of screw threads 19, one of the pair being formed on the nozzle forwardmost inner ledge or surface and the other on the fin rearmost outer surfaces. A flange 15 on a forward end of the nozzle 14 is of a size to engage and be received in an internal groove 16 in a rear portion of the gun 10. The groove 16 has a front side wall 17 which is longer than its rear side wall 18. Wall 17 takes some of the thrust imparted to the projectile 10 by the propellant pressure immediately after being fired and before such pressure has built up to a value high enough to expand the nozzle flange 15 into groove 16 and before the threads 19 on the nozzle and fins have become disengaged. The rear portion of the gun has a plurality of projections 28 of any desired angular extent. The projections 28 are biased inwardly by snap ring 20 for reception in a groove 21 on the rear outer surface of noz- 3,215,041 Patented Nov. 2, 1965 zle 14 for the purpose of holding the round including both the projectile 10 and the nozzle 14 against falling out the rear end of gun 10, particularly when its muzzle is steeply elevated. Those familiar with recoilless guns know that the venturi nozzle 14 has a forward taper or slope 22, a rearward taper or slope 23 and a constriction or throat 24.

In FIG. 2 is shown the same round immediately after firing by a few milliseconds and just before the projectile starts forward. At this time the propellant pressure acting on the forward slope 22 of nozzle 14 has expanded such nozzle portion an amount to engage the flange 15 far enough into groove 16 such that rear wall 18 of flange 15 will be engaged by the rear side wall of flange 15 and prevent the increasing propellant pressure from pushing the nozzle rearwardly. Since the threaded means 19 between nozzle 14 and projectile 10 cannot be disengaged at the exact instant the flange 15 engages wall 18, it is safer to have such flange 15 engage wall 18 of groove 16 before the threads 19 are disengaged. At this time the pressure is not a simple one of radial outward application because there is a forward pressure on the projectile opposed by threads 19 as well as by flange 15 and wall 17, and a forward component of pressure on taper 23 and a smaller rearward component of pressure on taper 22 and the wall 18. The threads 19 having sloping surfaces may be regarded as multipart cam surfaces tending to expand flange 15. A plurality of fins are provided and radially spaced equally about the longitudinally extending projectile axis.

According to FIG. 3 the projectile 11 has become disengaged from the nozzle 14 and propellant pressure is at a near peak, forcing flange 15 Well into groove 16, thus locking nozzle 14 against ejection by the rearwardly moving stream of igneous gases.

As shown in FIG. 4 the pressure Within nozzle 14 has been considerably reduced with the result the expansion stresses and their resulting strains have been so far reduced that with the projectile no longer in the gun, the flange 15 has become almost fully disengaged from wall 18 and the nozzle 14 is almost ready to be pushed rearward by the residual pressure within the gun which is fast dropping. As soon as the nozzle is relaxed enough and freed of pressure to be pushed rearwardly, the nozzle is free to be pushed that way.

FIG. 5 is a pressure-time curve showing conditions within the nozzle during one firing cycle. At the zero presure shown at point 29 before the propellant has been fired and the pressure begun to be formed, the outside diameter of flange 15 is a few thousandths of an inch smaller than the inside diameter of the portion of the gun that is adjacently rearward of groove wall 18 and surrounding the nozzle. At point 30 the nozzle has been expanded enough for flange 15 to have its rear wall engage wall 18 of groove 16 and the threads 19 just about to be disengaged from the projectile which is ready for its forward flight. At point 31 on the FIG. 5 graph the projectile has begun to move under a near peak of propellant pressure. This delay in forward motion of the projectile results in it having a higher acceleration and muzzle veloc ity than would be the case were its forward motion not delayed, and this practice is known in the art as a shot start. At about point 32 on the graph the nozzle has just been released from its holding groove 16. Pressure of propellant at point 32 may be called residual pressure, which is useful for ejecting the nozzle rearwardly from the gun.

After ejection, a nozzle 14 may again be attached to an unfired round for use over again until the internal throat diameter becomes objectionably Worn. The nozzle 14 is constructed so that when subjected to peak propellant pressure within the nozzle, the accompanying expansion will-not stress-the nozzle metal in tension above its elastic 1irnit'."Preferably,- the releasable connecting means19"on* the -fins-will-be stressed beyondits elastic limit. When stressed beyond its ultimate strength the nozzle may be broken into a number of pieces according to its configuration and material but'still'rem'oved by propellantpressure. Besides steel of a thickness to possess the desired'e'lastic' expansion, the nozzle may be made of other-elastic'materials. For example, aluminum is suitable-when coated with a high temperature protective material...

Instead of employing ordinary screw threads 19 betweenp then'ozzle and" projectile, FIG. 6 shows another embodiment in which one continuous longitudinal cam surface 25 is'provided instead of the plurality of short cam surfaces formedby. ordinary threads. Surface 25 and its mating recessed surface 26 on the forward end of the nozzle are inclined so that increased pressure tending tov movetheprojectile: forward assists in expanding the nozzle .flange 15 "radially outward: The surface 25 is able to expand flange 15: more easily than threads because the inclination. illustrated is more gradual and requires a greater longitudinal. movement of the projectile to expand the. nozzle the. desired amount, whereas the threads haveasteeper inclination in a much shorter distance. The FIG. '6lembodiment is not suitable where a maximum acceleration/and velocity are required and a mostieffective type. shot .start is needed. However, the FIG; 6 construction is desirable where lower than maximum acceleration'and velocity are desired in a projectile.

This invention is not limited for use with projectiles having. fins but "is also. suitable. with projectiles having suitable, centrally positioned ignition components. Either finned. projectilesbr other type projectiles are provided with anelectric or. percussion conductor 27, passing through the nozzle'into a primer 27a.

provided with a venturi nozzle secured to an end of said projectile, a propellant charge carried by said projectile and means for'igniting said propellant to fire said weapon and proj'ectile, the combinationther'ewith of the improvement enabling said nozzle to be released by pressure of said propellant and yet held: by. said gun until .after said projectilezhas been released from'said nozzle, said improvement including said nozzle being of a thin expansible metal provided with a shallow but secure flange, groove means at a forward portion of said nozzle for holding the same attached to said projectile, said weapon provided with an internal groove substantially radially aligned with said flange, and said nozzle flange being of a size for engagement in said Weapon groove, a forward wall of said weapon groove extending radially inward further than does a rear wall of the same groove to hold an unstressed nozzle against moving forward with said projectile, said nozzle possessing enough residual elasticity to shrink after reduction of propellant pressure and'be ejected by residual pressure after pressure reduction and forward movement of said projectile.

2. A combination according to claim 1 including yieldable means for holding a projectile in said weapon against sliding rearwardly when said weapon has its muzzle steeply elevated.

3. A combination according to claim 1 in which said nozzle is of steel. 1

4. A combination according to claim 1 in which said nozzle is of aluminum provided with a thermal protective coating.

5. A nozzle and projectile arrangement for unitary insertion' into a gun comprising,

aprojectile having a forward cartridge case and fins extending rearwardly therefrom, said fins having rearmost external thread means, and

a nozzle having a forwardmost portion containing an exterior flange and interior thread means in threaded engagement with said fin thread means, said nozzle being of a thin expansible metal,

so constructed and arranged that the forward portion of said nozzle, upon being subjected to interior propellant gas pressure, will expand radially to disengage said nozzle from said projectile.

References Cited by the Examiner UNITED STATES PATENTS 2,804,822 9/57 Meneghelli 102-49 2,970,520 2/61 Grandy 891.7 2,987,965 6/61 Musser 891.7 3,079,752 3/63 Thielman 60-35.6

SAMUEL FEINBERG, Primary Examiner.

SAMUEL W. ENGLE, Examiner, 

1. IN A BREECHLESS, RECOILLESS WEAPON HAVING A PROJECTILE PROVIDED WITH A VENTURI NOZZLE SECURED TO AN END OF SAID PROJECTILE, A PROPELLANT CHARGE CARRIED BY SAID PROJECTILE AND MEANS FOR IGNITING SAID PROPELLANT TO FIRE SAID WEAPON AND PROJECTILE, THE COMBINATION THEREWITH OF THE IMPROVEMENT ENABLING SAID NOZZLE TO BE RELEASED BY PRESSURE OF SAID PROPELLANT AND YET HELD BY SAID GUN UNTIL AFTER SAID PROJECTILE HAS BEEN RELEASED FROM SAID NOZLE, SAID IMPROVEMENT INCUDING SAID NOZZLE BEING OF A THIN EXPANSIBLE METAL PROVIDED WITH A SHALLOW BUT SECURE FLANGE, GROOVE MEANS AT A FORWARD PORTION OF SAID NOZZLE FOR HOLDING THE SAME ATTACHED TO SAID PROJECTILE, SAID WEAPON PROVIDED WITH AN INTERNAL GROOVE SUBSTANTIALLY RADIALLY ALIGNED WITH SAID FLANGE, AND SAID FLANGE BEING OF A SIZE OF ENGAGEMENT IN SAID WEAPON GROOVE, A FORWARD WALL OF SAID WEAPON GROOVE EXTENDING RADIALLY INWARD 